1. Field of the Invention
The present invention relates to the structure of a crankcase for an internal combustion engine. More specifically, to the structure of a crankcase for preventing dew condensation in the crankcase and preventing lubricating oil from being diluted by the inflow of condensed dew. In addition, the present invention relates to a crankcase emission control system of an internal combustion engine wherein a flow control valve that allows only a flow to the side of an intake system is provided on the way of a blowby gas passage connecting the intake system including an intake port provided to a cylinder head and a crankcase.
2. Description of Background Art
As difference in temperature between blowby gas that leaks out into a crankcase and the crankcase or lubricating oil is large when warming up is made in a situation where outside air temperature is low, steam and hydrocarbon included in the blowby gas are condensed into a dew in the crankcase. This dew is mixed with the lubricating oil and may dilute the lubricating oil. In operating the vehicle at the beginning of driving in a situation where outside air temperature is low, dew condensation and the dilution of lubricating oil may be also caused.
In JP-A No. 2004-218502 (FIG. 3), a technique is disclosed for heating cooling water for cooling an internal combustion engine when the internal combustion engine is started, for heating lubricating oil by the cooling water and for reducing the time for warming up. In this technique, the cooling water is made to flow into a cooling water passage for controlling the temperature of the lubricating oil is led into a heater passage and is heated there, and hereby, the lubricating oil is warmed.
In the related art, as cooling water is led into a heater passage and is heated there to heat the cooling water, a heater is required to be provided and the structure is complex.
In an internal combustion engine, a part of exhaust gas combusted in a combustion chamber leaks to the side of a crankcase from a clearance between an inside face of a cylinder bore and a piston as blowby gas. Thereafter, it is practical to use a technique for taking fresh air from an intake system into the crankcase, circulating blowby gas in the crankcase to the intake system and recombusting it in the combustion chamber.
As the performance of the engine is deteriorated when the quantity in which blowby gas is increased recklessly when it is circulated, a flow control valve that regulates the circulation of the quantity is provided on the way of a blowby gas passage. See, for example, JP-A No. 2004-245176.
However, the flow control valve disclosed in JP-A No. 2004-245176 is connected to an outlet of an oil separator provided to a crankcase and a cylinder head in the body of the engine that is attached to the outside face of a cylinder block and is connected on the way of an intake pipe connecting an air cleaner and an intake port via a hose. As the blowby gas passage from the crankcase to the intake pipe is long, the temperature of the blowby gas in the blowby gas passage is lowered and dew condensation may be caused.